KR100731036B1 - LCD with micro-lens - Google Patents

Abstract

The present invention relates to a liquid crystal display (LCD) device having a fine lens, which increases the process tolerance of a liquid crystal cell. More particularly, the present invention relates to a liquid crystal display , Thereby improving image quality and yield.

The liquid crystal display element preferably has the same transmittance in all the gradation steps with respect to the thickness variation. However, in the manufacturing process, the cell gap of the liquid crystal cell is uneven to some extent, and the transmittance is different due to this, and the image quality is deteriorated. A slit pattern 21 or a floating electrode 21 is formed by etching each electrode on the pixel electrode 5 or the common electrode 6 for applying a voltage to the liquid crystal layer in order to prevent the deterioration of image quality caused by unevenness in the thickness of the liquid crystal cell. Electrode 22 was placed. When the fine lens 3 is attached to increase the transmittance, the overall design should be performed in consideration of the alignment error.

In the present invention, the focal point of the fine lens is placed on the center symmetry line of the slit pattern or the floating electrode to minimize the change in transmittance due to the alignment error in the adhesion process. The liquid crystal display of the present invention can be applied as a display device of a liquid crystal projector that requires high brightness and high image quality like conference materials or HDTV.

Micro lens, slit pattern, liquid crystal cell thickness

Description

(LCD with micro-lens) < RTI ID = 0.0 >

1 is a schematic view of a liquid crystal projector.

Fig. 2 is a conventional liquid crystal display element with a fine lens attached thereto.

3 is a plan view of several electrodes of a conventional TFT liquid crystal cell pixel.

Fig. 4 is a liquid crystal display element of the present invention to which a fine lens is attached.

5 is a plan view of several electrodes of a pixel having a slit pattern.

6 is a plan view of several electrodes of a pixel having a floating electrode.

7 is a graph showing the transmittance change of each gradation with respect to the thickness variation of the liquid crystal cell of the present invention.

Fig. 8 is a graph showing a relative transmittance change with respect to an alignment error of a micro lens. Fig.

Fig. 9 is an explanatory diagram for obtaining the voltage distribution of the slit pattern. Fig.

  [Description of Drawings]

1,2 Glass substrate 3 Fine lens 4 Liquid crystal layer 5 Pixel electrode

6 common electrode 7 signal line 8 scanning line 10 liquid crystal display element

20 TFT 21 Slit pattern 22 Floating electrode

40 cross section of transmitted light 41, 42 symmetry line

The present invention increases the process tolerance of a liquid crystal cell in a liquid crystal display device having a fine lens, and minimizes a change in transmittance due to brightness and an alignment error with respect to a gray level.

1 is a schematic view of a liquid crystal projector.
The liquid crystal projector separates the white light from the light source 42 into red, blue, and green, passes through the liquid crystal panels 10R, 10G, and 10B that modulate the respective colors, is reunited, , And forms a picture on the screen (41). The white light emitted from the light source is divided into a red light, a blue light and a green light by a dichroic mirror 43, passes through a liquid crystal panel for adjusting the transmittance of light, is collected again in a color mirror, passes through a projection lens 44, As shown in FIG.
In FIG. 1, the lower case letters of the color mirrors 43 indicate the colors to be reflected. Red is r, green is g, and blue is b. In FIG. 1, the capital letters of the liquid crystal panels 10R, 10G, and 10B indicate that light of each color is modulated. The liquid crystal display element for modulating red is R, the liquid crystal display element for modulating green is G, and the liquid crystal display element for modulating blue is B. The liquid crystal projector is small in volume, easily adjusts the size of the screen, is excellent in color reproducibility, and is widely used as a large display device such as an HDTV or a seminar presentation screen.

In a liquid crystal display device used in a liquid crystal projector, an active element for applying and blocking a voltage to the liquid crystal layer is attached to each pixel. Among the active matrix LCDs, the TFT liquid crystal display device is most commonly used as a screen element of a liquid crystal projector due to the ease of gradation implementation and quick response characteristics.

2 is a sectional view of a liquid crystal display element for a liquid crystal projector to which a fine lens 3 is attached.
The fine lens enhances the effective aperture ratio by sending light coming into a region where the BM (Black Matrix), a signal line, a scanning line or the like can not be modulated, to the pixel electrode 5 side.
Fig. 3 is a plan view of various electrodes of the TFT liquid crystal cell pixel of Fig. 2, in which the scanning line 8, the signal line 7, and the pixel electrode 5 are arranged.
The gate electrode of the TFT 20 in each pixel is connected to the scanning line 8, the source electrode to the signal line 7, and the drain electrode to the pixel electrode 5, respectively. A liquid crystal layer 4 is provided between the common electrode 6 and the pixel electrode 5.
The operation principle of the TFT liquid crystal panels 10R, 10G, and 10B is as follows.
During the selection period, a voltage higher than the signal line is applied to the gate electrode connected to the scanning line, and the connection resistance of the channel between the drain electrode and the source electrode is reduced, so that the voltage caught by the signal line is caught in the liquid crystal layer through the pixel electrode. During the non-selection period, a voltage lower than the signal line is applied to the gate electrode connected to the scanning line, and the drain electrode and the source electrode are electrically disconnected, so that the charges accumulated in the liquid crystal layer during the selection period are maintained. Scanning lines are sequentially scanned, and each pixel electrode is charged through a signal line to apply a voltage to the liquid crystal layer. When the root mean square (rms) voltage applied to the liquid crystal layer between the pixel electrode and the common electrode is adjusted, the polarized state of the linearly polarized light passing through the polarizing plate passes through the liquid crystal layer, and the light is selectively transmitted through the plate, As shown in FIG. The liquid crystal mode of the liquid crystal projector mainly uses a 90 ^° TN mode for a transmissive type, an ECB (Electric Controlled Birefringence) mode for a reflective type, or a TN mode for which a twist angle is less than 90 ^° .

Liquid crystal display devices of liquid crystal projectors are increasingly getting higher resolution, and 0.7-inch XGA class is now commercialized, and a 0.5-inch XGA liquid crystal display device is expected to be developed in the future. The higher the resolution, the lower the aperture ratio and the lower the brightness (brightness). The fine lens 3 is attached to the liquid crystal cell as shown in Fig.

Since it is difficult to make the thickness of the liquid crystal cell constant in the process of making the liquid crystal cell, the thickness of the liquid crystal cell varies to some extent depending on the position of the same liquid crystal panel. Also, since a large amount of infrared rays are emitted from the light source, the thickness of the liquid crystal cell is changed by the difference of thermal expansion depending on the position of the same liquid crystal panel. If the temperature difference between the upper and lower glass substrates 1 and 2 of the liquid crystal panel is 1 占 폚, the change in thickness of the liquid crystal cell is about 0.1 占 퐉. When the screen is bright, the difference in transmittance is small depending on the thickness of the liquid crystal cell, but the lower the gray level, the greater the change in the transmittance depending on the thickness of the liquid crystal cell.
FIG. 7 is a graph showing a change in transmittance of each liquid crystal cell with respect to a change in thickness of the liquid crystal cell.
Fig. 7 is based on the assumption that the thickness of the liquid crystal cell is 4.0 占 퐉, (a) is the thickness of 4.4 占 퐉, and (d) is 3.6 占 퐉. It can be seen that the difference is more than 40% depending on the thickness.
A slit pattern 21 or a floating electrode 21 is formed by etching each electrode on the pixel electrode 5 or the common electrode 6 for applying a voltage to the liquid crystal layer in order to prevent the deterioration of image quality caused by unevenness in the thickness of the liquid crystal cell. An attempt to place the electrode 22 was studied. In the case of attaching a fine lens, the overall design should be performed considering the misalignment of the adhesion process.
In the present invention, the focal point of the fine lens is placed on the center symmetry line of the slit pattern or the floating electrode to minimize the change in transmittance due to the alignment error in the adhesion process.

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The present invention relates to a liquid crystal display (LCD) device having a fine lens, which increases the process tolerance of a liquid crystal cell. More particularly, the present invention relates to a liquid crystal display , Thereby improving image quality and yield.
In the present invention, a pixel electrode 5 for applying a voltage to a liquid crystal layer is etched to form a slit pattern 20 and a floating electrode 21. The degradation of the image quality due to the variation of the transmittance with respect to the thickness change of the liquid crystal cell and the alignment error of the laminating process is minimized by using the side electric field properties according to the change of the thickness of the liquid crystal cell.
A study of the liquid crystal orientation when a slit pattern is placed on the pixel electrode has been extensively studied since IBM's Lien published it in SID in 1992 (SID 92 DIGEST p33). Until now, the liquid crystal has been mainly made into a multi-domain by using a slit pattern, and is limited mainly to a portion where the viewing angle is widened. The inventor of the present patent application filed a patent in 1999 (Patent Application No. 10-1999-0016499) that the process tolerance of the thickness of the TN liquid crystal cell was increased by using the slit pattern.

The voltage distribution in the slit pattern can be obtained by a simple formula.
9 is an explanatory diagram for obtaining an electric field and a voltage distribution induced in the slit pattern.
It is assumed that the voltage distribution in the slit pattern A has a circular shape as shown in Fig. An electrode having a plurality of voltage distributions (V1, V2, V3 ....) is placed around the microelectrode and if the capacitances (C1, C2, C3 ...) formed by the respective electrodes and the microelectrode are known , The induced voltage V (A) of part A can be obtained by the following equation.

In Fig. 9, it is assumed that V1 and V3 are the voltage of the pixel electrode, and V2 is the voltage of the common electrode. If the voltage distribution of the fine electrode portion of A is different from the voltage distribution (V1, V3, V1 = V3) of the pixel electrode, a horizontal electric field of the voltage corresponding to the difference is applied between the A region and the pixel electrode. When the thickness of the liquid crystal cell is reduced, the storage capacitance C2 between the fine electrode and the common electrode increases, so that V (A) moves toward the voltage of the common electrode. Conversely, when the thickness of the liquid crystal cell increases, Moves toward the voltage distribution of the pixel electrode.
In the case where the dielectric constant anisotropy of the liquid crystal is positive and the side electric field and the vertical electric field are simultaneously applied, when the side electric field is floated, the liquid crystal molecules tend to be oriented in a horizontal direction. On the other hand, It becomes strong. When the thickness d of the liquid crystal cell is reduced, the horizontal electric field becomes large and the refractive index anisotropy of the liquid crystal becomes large. On the contrary, when the thickness d of the liquid crystal cell becomes large, the vertical electric field component becomes large The refractive index anisotropy becomes small. Therefore, since the transmittance of the liquid crystal cell is a function of DELTA d, DELTA n and d move in opposite directions, so that the change of DELTA d is reduced when there is a slit pattern, and the change of transmittance of the liquid crystal panel to the change of thickness of the liquid crystal cell is reduced.

Even when the floating electrode 21 is provided in the pixel electrode instead of the slit pattern, the voltage induced in the floating electrode is the same as the formula (1). It is possible to know the voltage of the floating electrode by calculating the storage capacitance formed between the floating electrode and the peripheral electrode rather than the fine region. Similarly, when the thickness d of the liquid crystal cell is reduced, the voltage induced in the floating electrode moves toward the voltage of the common electrode, so that the horizontal electric field becomes large to increase the refractive index anisotropy of the liquid crystal, The voltage induced in the floating electrode moves toward the voltage of the pixel electrode, so that the refractive index anisotropy becomes small. Since the brightness of the liquid crystal cell is a function of DELTA n, the transmissivity of the liquid crystal panel is insensitive to the change of the thickness of the liquid crystal cell, as in the case where the slit pattern exists even in the presence of the floating electrode since? N and d move in opposite directions.

4 is a cross-sectional view of the TFT liquid crystal display element used in the liquid crystal projector of the present invention.
4 is different from that of FIG. 2 only in the shape of the pixel electrode, and the remaining portions are the same. A cross-sectional view of the pixel electrode in Fig. 4 is shown in Fig.
4 and 5, the slit pattern 20 is formed to pass through the front and rear surfaces of the pixel electrode 5, and the floating electrode 21 is formed inside the slit pattern 20, As shown in FIG. Specifically, the slit pattern is designed so that the center of the cross section 40 of the light passing through the fine lenses comes to a symmetric point where the X-axis symmetry line 41 of the slit pattern and the Y-axis symmetry line 42 meet. The symmetry line bisecting the long axis direction of the slit pattern is the center line.
In Fig. 5, the X-axis symmetry line 41 is a center symmetrical line, and Fig. 6 is a sectional view of a pixel electrode including a floating electrode.
The slit pattern is designed such that the center of the cross section 40 of the light passing through the fine lenses comes to a symmetric point where the X axis symmetry line 41 of the floating electrode and the Y axis symmetry line 42 meet. This condition can minimize the change in transmittance to the alignment error. If the microscopic lens can not be focused on the point where the symmetry line of the X axis and the Y axis meet due to the structure of the pixel or the fine lens, a point is selected from the center symmetry line.

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The slit pattern and the floating electrode may be placed on the common electrode. When the slit pattern 20 and the floating electrode 21 are disposed on the pixel electrode 5, since the pixel electrode can be formed simultaneously in the process of forming the pixel electrode, there is no additional process. However, when the common electrode 6 is provided with the slit pattern 20 and the floating electrode 21, since the common electrode is exposed, the exposure process is added one step as the case may be.

 7 is a graph showing a change in transmittance of each gradation with respect to a change in thickness of the liquid crystal cell. The thickness of the liquid crystal cell was 4.0 占 퐉, (a) is the thickness of 4.4 占 퐉, and (d) was 3.6 占 퐉. (B) and (c) show thicknesses of 4.4 .mu.m and 3.6 .mu.m, respectively, and the focus width of the fine lens was 4 .mu.m, which is the same as the width of the slit pattern, This is a change in transmittance of each liquid crystal projector using a liquid crystal display element having the same structure. The criterion is that the thickness of the liquid crystal cell is 4.0 占 퐉. It can be seen that the degree of change in transmittance with respect to the thickness variation of the liquid crystal cell is reduced for all the gradation steps.

If a micro lens is attached, the overall design should be done considering the alignment error. According to the present invention, it is possible to minimize the change in transmittance due to the alignment error in the laminating process by placing the focal point of the micro lens at the symmetrical point of the slit pattern or the floating electrode. 8 is a graph showing the relative luminance change rate with respect to the misalignment error of the fine lenses in the gradation step 96. FIG. And shows the relative change rate of the transmittance by integrating the transmittance within a radius of 2 占 퐉 every 0.25 占 퐉 around the central symmetry line. The integral value of the transmittance of 2 占 퐉 at the center of x is I (x) and the integral value of the transmittance of 2 占 퐉 at the center of 1 占 퐉 away from x is I (x +1), the relative permeability change rate R (x) in FIG. 8 is expressed by the following equation.

It can be seen that the relative transmittance change due to the alignment error is the smallest when the light passing through the fine lens is based on the slit pattern or the center symmetry line of the floating electrode.

If the light passing through the micro-lens goes out of the slit pattern, the effect of the slit pattern is not seen, so the light passing through the micro-lens is designed and controlled to pass through the slit pattern or the floating electrode. If the width of the slit pattern or the floating electrode is large, the driving voltage is increased and the contrast ratio is lowered, so that it is designed to be smaller than the thickness of the liquid crystal cell. Since the thickness of the liquid crystal cell is about 4 占 퐉, the width of the slit pattern is 4 占 퐉, which is the most suitable in terms of driving voltage and contrast ratio. Under these conditions, the light past the fine lens must be within 2 탆 of the central symmetry line 41 (42) to pass the slit pattern.

The liquid crystal display of the present invention can be applied as a display device of a liquid crystal projector which requires high brightness and high image quality like conference materials or HD TV.

Claims (4)

An active element formed in each pixel; A pixel electrode connected to the active element; A slit pattern formed to pass through the front and rear surfaces of the pixel electrode; A floating electrode formed inside the slit pattern and separated from the pixel electrode; A liquid crystal display element including a fine lens collecting light into a transmissive region of each pixel, And a light passing through the micro lens passes through a center symmetry line of the floating electrode. The method according to claim 1, Wherein a distance between a center of the light passing through the fine lens and a center symmetry line of the slit pattern or the floating electrode is 2 占 퐉 or less. An active element formed in each pixel; A pixel electrode connected to the active element; A slit pattern formed to pass through the front and rear surfaces of the pixel electrode; And a fine lens that collects light into a transmissive region of each of the pixels, And the light passing through the micro lenses passes through the center symmetry line of the slit pattern. The method of claim 3, Wherein a distance between a center of the light passing through the minute lenses and a center symmetry line of the slit pattern is 2 占 퐉 or less.

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